This invention relates to refrigeration apparatus and a refrigeration process and more specifically relates to a novel refrigeration apparatus and process employing a mixture of different refrigerants.
Refrigeration systems are well known which employ a single refrigerant, for example, CFC refrigerants such as R-12 and HCFC refrigerants such as R-22. These refrigerants, however, have serious environmental drawbacks and are being replaced by refrigerants of the HFC type such as R-32, R-125 and R-134a in different combinations.
The individual HFC refrigerants have diverse characteristics, as shown in the following table:
In many refrigeration systems, the following characteristics are preferred:
Densityxe2x80x94heavy
Boiling Pointxe2x80x94low at evaporator and high at condenser
Latent Heatxe2x80x94large
Condenser Pressurexe2x80x94low
Evaporator Pressurexe2x80x94high
Heat Transferxe2x80x94good
Flamabilityxe2x80x94no
In the above, hfg is the enthalpy difference between 100% vapor and 100% liquid.
R-32 is a preferred refrigerant because of its high latent heat and high evaporator pressure which reduces the compressor work and thus the compressor size. That is, the compressor work WCOMPRESSOR is defined as:
WCOMPRESSOR=∫vdP
where
v=specific volume=1/density; and
P=pressure.
In a typical system, as evaporator pressure increases, the pressure change in the compressor is reduced, thus reducing the compressor work.
While R-32 has the best thermal characteristics, it is more flammable than the others, and carries with it the danger of fire. Consequently, R-32 is commonly mixed with non-flammable fluids such as R-125 and R-134a to reduce the fire danger.
Currently available mixture refrigerants include R-407c and R-410a. The former (R-407c) is one of the R-407 series refrigerants, which include R-407a, R-407b, R-407c, etc. The R-407 series is made of three refrigerants R-32, R-125 and R-134a. The last letter in the designation of R-407 indicates different composition ratios of R-32, R-125 and R-134a. For example, R-407c is made of R-32, R-125 and R-134a at a ratio of 23:25:52 based on mass. Similarly, R-410a is one of the R-410 series refrigerants which are made of two refrigerants R-32 and R-125. The last letter xe2x80x9caxe2x80x9d in R-410a indicates that a composition ratio of R-32 and R-125 is 50:50 by mass. Depending on the composition ratio, the last letter can vary.
Several new HFC type refrigerants such as R-134a, R-407c and R-410a are known in attempts to get the best trade-off of flammability versus thermal efficiency. The first R-134a has replaced R-12 for automotive air conditioners, refrigerators and large chillers. This refrigerant has relatively poor heat transfer characteristics but in a typical system produces a pressure of about 8 atm at the evaporator and 16 atm at the condenser. Thus, the relatively small xcex94P at the compressor produces excellent efficiency. Therefore, this refrigerant has replaced R-12 for many applications, despite its poor heat transfer characteristics.
A second HFC type refrigerant is R-407c, which is a mixture of R-32, R-125 and R-134a in proportions of 23:25:52 respectively. This mixture, however, produces only about 6 atm at the evaporator and 20 atm at the condenser (like R-22) and has poor heat transfer characteristics due to the high proportion of R-134a.
A third HFC type refrigerant is R-410a, which is a mixture of R-32 and R-125 in a ratio of 50:50 respectively. This mixture, however, produces about 12 atm at the evaporator, but 30 atm at the condenser and requires a large compressor and compressor work.
It would be very desirable to provide a novel refrigeration system which would permit the use of a non-flammable mixture of refrigerants, a reduced condenser pressure and an increased evaporator pressure; and which takes the best advantage of the properties of the individual fluids of the mixture.
In accordance with the invention, a novel system and refrigeration process is provided in which a first component (for example, R-134a) is recirculated in the condenser while the other component or components (for example, R-32 and R-125) are directed, without recirculation, to the evaporator to increase evaporator pressure and heat capacity. The composition of the circulating refrigerant may be controlled, as by a valve, in the recirculation path to effectively control thermal load variation.
In a preferred embodiment of the invention, the condenser is divided into two sections, with a vortex tube or other liquid-vapor separator between them to recirculate the liquid R-134a through the first condenser structure.
The vortex tube, or the like, between condenser sections will:
1. Promote liquification in the first condenser by recirculating R-134a rich liquid into the first condenser section;
2. Pass vapor to the second condenser section which is rich in R-32 and R-125;
3. Follow thermal load variation by controlling the amount of recirculating R-134a.
In the novel system, liquid is returned to the inlet of the condenser using the vortex tube as a pump. Other pumps can be used, including venturi tubes.
The advantages produced by the invention include:
1. The use of a non-flammable fluid;
2. A large heat capacity at evaporator;
3. A lower condenser pressure;
4. A higher vapor pressure in the evaporator, producing a lower specific volume v in the evaporator, thus reducing compressor work ∫vdP.
As a result of the above, the system requires lower compressor work to reduce compressor size, and produces higher latent heat in the evaporator, producing a more efficient evaporator.
In accordance with the specific improvements of the instant application, several features are superimposed on the basic concepts.
Thus, in a first improvement, a superheated mixture vapor is taken from the compressor output and is injected into the liquid volume of a liquid-vapor separator, producing highly enriched R-134a in the regenerative line.
As a second improvement, the high boiling point refrigerant component, for example, R-134a is recirculated around both the compressor and the condenser producing increased subcooling of the R134a component. At the same time the suction pressure of the compressor is increased through the use of a secondary expansion device which reduces condenser pressure to an intermediate value that is still greater than the evaporator pressure. The benefit of this improvement is increased subcooling, increased suction pressure at the compressor, and increased EER.
As a still further improvement and also to obtain increased subcooling, increased suction pressure at the compressor and increased EER, the novel regenerative concept can also be applied to a single refrigerant system such as R-22 only.
In general, in order to increase the concentration of the high-boiling point refrigerant (i.e., R-134a) in the liquid of the liquid-vapor separator, a superheated mixture vapor tapped from a line between the compressor and the first condenser is directly injected to a liquid inside the liquid-vapor separator. An adjustable valve controls the amount of the superheated mixture vapor injected so that one can vary the concentration of the high-boiling point refrigerant (i.e., R-134a) in the recirculation line.